Difference Between Gravity and Magnetism

Posted on September 16, 2011 by admin Last updated on: September 17, 2011

Gravity vs Magnetism

Gravitational force and magnetic forces are two of the most fundamental forces the universe is built upon. It is very important to have a sufficient understanding in these fundamental forces in order to understand the mechanics of the universe. Gravity along with electromagnetic force, weak nuclear force and strong nuclear force makes up the four fundamental forces of the universe. These theories play a vital role in fields such as cosmology, relativity, quantum mechanics, astronomy, astrophysics, particle physics and almost anything that is in the known universe. In this article, we will discuss the theories behind gravity and magnetism, their similarities, how they occur in the universe and finally their differences.

Gravity

Gravity is the force that occurs due to any mass. Mass is the necessary and the sufficient condition for gravity. There is a gravitational field defined around any mass. Take masses m1 and m2 placed in a distance r from one another. The gravitational force between these two masses is G.m1.m2 / r^2 where G is the universal gravitational constant. Since negative masses are not present, the gravitational force is always attractive. There are no repulsive gravitational forces. It must be noted that gravitational forces are also mutual. That means the force m1 exerts on m2 is equal and opposite to the force m2 is exerting on m1.

The gravitational potential at a point is defined as the amount of work done on a unit mass when bringing it from infinity to the given point. Since the gravitational potential at infinity is zero, and since the amount of work has to be done is negative the gravitational potential is always negative. Therefore, the gravitational potential energy of any object is also negative.

Magnetism

Magnetism occurs due to electric currents. A straight current carrying conductor exerts a force normal to the current on another current carrying conductor placed parallel to the first conductor. Since this force is perpendicular to the flow of charges, this can’t be the electric force. This was later identified as magnetism. Even the permanent magnets we see are based on the current loop created by the spin of the electron.

The magnetic force can be either attractive or repulsive, but this is always mutual. A magnetic field exerts a force on any moving charge, but stationary charges are not affected. A magnetic field of a moving charge is always perpendicular to the velocity. The force on a moving charge by a magnetic field is proportional to the velocity of charge and the direction of the magnetic field.

What is the difference between magnetism and gravity?

• Gravitational forces occur due to mass and magnetism occurs due to moving charges.

• Magnetic forces can be either attractive or repulsive, but gravitational forces are always attractive.

• Applying the Gauss’ law to masses gives the total gravitational flux over the closed surface as the mass is enclosed, but this applied to the magnets always yields zero.

• Since there are no magnetic monopoles, the total magnetic flux over any closed surface is always zero.